Curable epoxy resin compositions and use in preparing formed, shaped, filled bodies

ABSTRACT

Curable epoxy resin compositions are described which comprise a mixture of an acid curable epoxy resin and a minor amount of an oxidizing agent capable of reacting with sulfur dioxide to form a catalyst for curing said epoxy resin. The curable epoxy resin composition may contain solid particulate materials. The procedures for curing such epoxy resins as well as methods for forming sand cores and molds also are described. Sand cores and molds produced in accordance with the method of the invention have sufficient strength and hardness after a few seconds of curing for normal foundry applications.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 703,090, filed on Mar. 29,1985, now abandoned, which is a divisional of application Ser. No.436,031, filed on Oct. 22, 1982, now U.S. Pat. No. 4,518,723, which is acontinuation-in-part of application Ser. No. 405,720, filed on Aug. 5,1982, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to new and useful curable epoxy resincompositions comprising acid curable eposy resins and a minor amount ofan oxidizing agent which is capable of reacting with sulfur dioxide toform a catalyst for curing said epoxy resin. These curable epoxy resincompositions are useful particularly in preparing formed, shaped, filledbodies which comprise the epoxy resin and inorganic solid particulates.Particularly useful filled bodies of this type include abrasivearticles, foundry cores and molds.

Over the last several decades, the so-called "epoxy" resins have gainedwide acceeptance in various arts. Epoxy resins possess unusually goodelectricl, thermal and chemical properties and exhibit low shrinkageduring cure. Epoxy resins provide good adhesion to a variety of surfacesof materials, and, consequently, they have been particularly effectivein coatings, electronic and electridal applications, and as binders andadhesives in a number of applications. Epoxy resins are characterized bythe presence therein of an epoxide group, i.e., ##STR1## wherein x is asmall whole number. Such resins are available commercially from a widevariety of sources. Commercially available products, depending upon thechemical makeup of the epoxy resin, are characterized by a variety ofproperties.

Epoxide resins are converted to useful forms through condensationreactions which are initiated and/or promoted by means of heat and/or acondensing catalyst or curing agent. Conventionally, the epoxy resinsare marketed in the form of liquid or solid compositions comprising thepartially condensed resin which may or may not contain the curing agent.A final cure to a solid usable form is effected at the time of use, if acatalyst is present, by heating the composition to a moderately elevatedtemperature. In many instances, the commercially available epoxy resincompositions will not contain the curing agent or hardener because manycuring agents have a certain degree of activity at ambient temperatures,and consequently such compositions would have an undesirable shortstorage life. Accordingly, producers of epoxy resins sell hardenerpackages for use with epoxy resins and, generally, such hardeners orcuring agents are added to the epoxy resin when it is desired to curethe resin to a solid usable form.

Another method for effecting the cure or hardening of epoxide resins,particularly at ambient temperatures and without requiring theincorporation of a curing agent in the composition itself have beendescribed. For example, in U.S. Pat. No. 3,139,657, epoixde resincompositions are cured through the use of normally gaseous curingagents. Examples of such curing agents include certain inorganicnitrogen and halogen compounds such hydrogen halides, boron-halogencompounds, silica-halogen compounds and nitrogen-halogen compounds. Itis essential, however, that the epoxide composition be in contact with asolid heat absorbent during its treatment with the gaseous curing agentand that the epoxide compositions be in the form of a thin film with itssurface area exposed for contact with a gaseous agent. The patenteesstate that films greater than about 0.01 inch thickness cannot becompletely cured by this process.

In the foundry industry, sand is coated with resin binders and formedinto molds and cores for the production of precision castings. A widevariety of techniques has been developed for the manufacture of sandcores and molds. These involve the hot bos technique for mold and coreformation; the shell method; the "No-Bake", and the cold-box technique.

In the hot box and shell methods, sand molds and cores are formed byheating a mixture of sand with a thermosetting resin at a temperature ofabout 150°-320° C. in contact with patterns which produce the desiredshape for the mold or core. The resin is polymerized and a core or moldis formed. Procedures of this type are described in Dunn et al U.S. Pat.No. 3,059,297 and Brown et al U.S. Pat. No. 3,020,609.

A particular disadvantage of the hot box and shell methods is thenecessity for heating the pattern boxes to 150°-320° C. to polymerizeand cure the resin binder. This involves considerable expense and isgenerally a high cost technique.

The cold box techniques for core and mold formation involve the use ofsand mixed or coated with resins which may be cured at room temperatureby acid or base catalysis. Acid or base catalyst have been used inliquid, solid or gaseous form. Typical cold box processes are shown inBlaies U.S. Pat. No. 3,008,205; Dunn et al U.S. Pat. No. 3,059,297;Peters et al U.S. Pat. No. 3,108,340; Brown et al U.S. Pat. No.3,184,814; Robins U.S. Pat. No. 3,639,654; Australian Pat. No. 453,160and British Pat. No. 1,225,984. Many of these processes involve the useof sulfur-containing acid catalyst such as benzene sulfonic acid,toluene sulfonic acid and the like.

A few years ago, a process was developed for room temperaturepolymerization of condensation resins in which an acid-curing agent isgenerated in situ in the resin or on a sand-resin mix. It had previouslybeen suggested in U.S. Pat. No. 3,145,438 to inject SO₃ in a form of agas into a mixture of sand and resin to cure the resin at roomtemperature. It was found, however, that this process causes aninstantaneous curing of the resin in the region subjected to treatmentby SO₃ which impedes the diffusion of this gas to other parts of theresin, particularly the central parts of the mixture.

Subsequently, a method was developed which avoided this difficulty. InRichard U.S. Pat. No. 3,978,339, it is disclosed that sand may be coatedwith a suitable oxidizing agent, such as an organic peroxide, and coatedwith the resin to be used in binding the sand into the form of a core ormold. The sand-resin mixture is then formed into suitable shape andtreated with gaseous SO₂. The SO₂ is oxidized, in situ, to SO₃ andconveted to sulfur-containing acid by water present in the mixture. Thesulfure-containing acid which is generated in situ causes a raid anduniform polymerization of the resin at room temperature. This processhas proved successful commercially and has been applied to phenolicresins, furan resins, and urea-formaldchyde resins, as well as mixturesand copolymers thereof.

In the cold box method of Richard U.S. Pat. No. 3,879,339, there are alarge variety of peroxides disclosed which may be added to sand alongwith resins which are used in forming sand cores or molds. Thiscomposition is subsequently formed into shape and treated with gaseousSO₂. The peroxides which are disclosed in the Richard patent are mostlyquite expensive and, in many cases, are difficult to handle and to shipor transport. Organic peroxides require special approval fortransportation in interstate commerce. Organic peroxides are oftenhighly flammable or present other fire hazards. Organic peroxdies alsoare often shock sensitive and may explode or detonate under certainconditions. As a result, not all organic peroxides can be used in theRichard process because of economic and safety considerations.

The prior art discloses some application of epoxy resins to themanufacture of foundry cores and molds but these resins usually requirethe use of strong acid gases for curing which can give rise to seriousproblems, e.g. corrosion, etc., with the equipment and difficulties inthe use of the epoxy bonded products.

Kottle et al U.S. Pat. No. 3,145,438 discloses a gaseous curing processfor curing resins for binding sand and abrasive granules, i.e. sandcores and molds. The resins disclosed are primarily furfuryl alcoholformaldehyde resins and also certain epoxy resins including epoxidizedlinseed oil, mono- and divinylcyclohexene dioxide, butadiene dioxide,glycidyl methacrylate and its polymers. The curing gases are strong acidgases including boron trifluoride, boron trichloride, hydrogen chloride,sulfur trioxide.

Moore U.S. Pat. No. 3,107,403 discloses the preparation of sand cores ormolds using epoxy resins in which the molding composition is cured bytreatment with a strong Lewis acid, such as boron trifluoride, titaniumtetrachloride, tin tetrachloride, etc.

Walker et al U.S. Pat. No. 3,428,110 discloses a process for preparingsand cores and molds using polyisocyanates and a curable resin, e.g.phenolic, which is cured by treatment with a gaseous amine.

Bickerdike et al U.S. Pat. No. 3,519,056 discloses a method ofmanufacturing a mold for metal casting in which the mold is formed ofmineral fibers and includes a thermosetting resin including an epoxyresin or a phenolic resin. The resins are cured at a high temperature.

Stewart et al U.S. Pat. No. 4,176,114 discloses the preparation onfoundry cores and molds using resins modified with polyfurfuryl alcohol.The sand is treated with resin and an organic peroxide or hydroperoxideand the gassed with sulfur dioxide.

Steinbacher U.S. Pat. No. 4,050,500 discloses a shell molding processusing a soluble silicate, such as sodium silicate, as a binder. Thesodoum silicate is used to bind the sand in addition to a thermosettingorganic resin. The resins are cured by treatment with peroxides such asbenzoyl peroxide or t-butyl perbenzoate.

British Pat. No. 2,066,714 describes processes for preparing shapedfoundry articles using a binder material which comprises anethyleincally unsaturated monomer and curing by means of a free radicalinitiator. The initiator comprises an organic peroxide and a catalyticagent such as sulfur dioxide. Examples of monomers described as beinguseful include acrylates, and modified acrylate copolymers such asepoxy-acrylates, polyether-acrylates, polyester-acrylates andpolyester-urethane-acrylates.

SUMMARY OF THE INVENTION

The present invention relates to new and useful curable epoxy resincompositions comprising a mixture of an acid curable epoxy resin and aminor amount of an oxidizing agent which is capable of reacting withsulfur dioxide to form a catalyst for curing said epoxy resin. Theinvention also relates to methods for curing said epoxy resins and theuse of such curable epoxy resins in the preparation of formed shapedfilled bodies. The curable epoxy resins of the invention have been foundto be useful particularly in the formation of foundry cores and moldssuch as sand cores or molds.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The compositions of this invention are curable epoxy resin compositionswhich comprise a mixture of an acid curable epoxy resin and a minoramount of an oxidizing agent capable of reacting with sulfur dioxide toform a catalyst for curing said epoxy resin.

The epoxy resins utilized in the invention may be any one of a number ofwell known resins which are acid-curable and which are characterized bythe presence therein of an epoxide group, i.e., ##STR2## wherein x iszero or a small whole number. Such resins have either a mixed aliphaticaromatic or an exclusively non-benzenoid (i.e., aliphatic orcycloaliphatic) molecular structure. The mixed aliphatic-aromatic epoxyresins generally are prepared by the well-known reaction of abis-(hydroxy-aromatic) alkane or a tetrakis-(hydroxy-aromatic) alkanewith a halogen-substituted aliphatic epoxide in the presence of a basesuch as, for example, sodium hydroxide or potassium hydroxide. Examplesof the halogen-substituted aliphatic epoxides include epichlorohydrin,4-chloro-1,2-epoxy-butane, 5-bromo-1,2-epoxypentane,6-chloro-1,3-epoxyhexane and the like. In general, it is preferred touse a chlorine substituted terminal denoting that the epoxide group ison the end of the alkyl chain.

The most widely used epoxy resins are diglycidyl ethers of bisphenol A.These are made by epichlorohydrin with bisphenol A in the presence of analkaline catalyst. By controlling the operating conditions and varyingthe ratio of epichlorohydrin to bisphenol A, products of differentmolecular weight can be made.

Other usable epoxy resins include the diglycidyl ethers of otherbisphenol compounds such as bisphenol B, F, G and H.

Epoxy resins of the type described above based on various bisphenols areavailable from a wide variety of commercial sources. One group is knownby the general trade designation "Epon" resins and are available fromShell Chemical Company. For example, "Epon 820" is an epoxy resin havingan average molecular weight of about 380 and is prepared from2,2-bis-(p-hydroxyphenol) propane and epichlorohydrin. Similarly, "Epon1031" is an epoxy resin having an average molecular weight of about 616and is prepared from epichlorohydrin and symmetricaltetrakis-)p-hydroxyphenol) ethane. "Epon 828" has a molecular weight of350-400 and an epoxide equivalent of about 175-210.

Another group of commercially available epoxy resins is identified underthe general trade designation EPI-REZ (Celanese Resins, a division ofCelanese Coatings Company). For example, EPI-REZ 510 and EPI-REZ 509 arecommercial grades of the diglycidyl ether or bisphenol A differingslightly in viscosity and epoxide equivalent.

Another class of epoxy resins useful in the present invention is thenovolacs, particularly the epoxy cresol and epoxy phenol novolacs. Theseare produced by reacting a novolac resin, usually formed by the reactionof orthocresol or phenol and formaldehyde with epichlorohydrin.

Epoxy resins derived from non-benzenoid materials such as aliphatic orcycloaliphatic hydroxy-containing compounds also can be utilized in thepresent invention. Epoxy resins having non-benzenoid molecularstructures generally are referred to in the art as being aliphatic epoxyresins or cycloaliphatic epoxy resins. Cycoaliphatics can be produced bythe peracetic epoxidation of cyclic olefins and by the condensation ofan acid such as tetrahydrophthalic with epichlorohydrin, followed bydehydrohalogenation. The aliphatic epoxy resins can be prepared byreacting hydroxy-containing aliphatic and cycloaliphatic compounds suchas aliphatic diols and triols. For example, ethylene glycol or glycerolcan be reacted with a halogen-substituted aliphatic epoxide such asepichlorohydrin (and others mentioned above) to form liquid epoxy resinscharacterized by viscosities which are lower than epoxy resins derivedfrom aromatic hydroxy compounds. When cured, such aliphatic epoxy resinsare not as brittle as the aromatic epxoy resins, and in many instances,exhibit elastomeric properties. Aliphatic epoxy resins are availablecommercially from a variety of sources including, for example, ShellChemical Company and Reichhold Chemicals, Inc. Specific examples includeEpon 562 from Shell Chemical Company having a viscosity of 90-150centipoises at about 23° C., an epoxide equivalent of 140-165, and ahydroxyl equivalent weight of about 65.

In accordance with the present invention, an oxidizing agent is includedas a curing or hardening agent in the acid curable epoxy resinformulations. The oxidizing agents which are incorporated into the acidcurable epoxy resin compositions of the invention are oxidizing agentswhich will react with sulfur dioxide to form a catalyst of curing theepoxy resin.

Numerous oxidizing agents are suitable for use with the epoxy resins ofthe invention. Suitable agents include peroxides, hydroperoxides,hydroxy hydroperoxides, chlorates, perchlorates, chlorites,hydrochlorides, perbenzoates, permanganates, etc. Preferably, however,the oxidizing agent is a peroxide, hydroperoxide or a mixture of aperoxide or hydroperoxide with hydrogen peroxide. The organic peroxidesmay be aromatic or alkyl peroxides. Examples of useful diacyl peroxidesinclude benzoyl peroxide, lauroyl peroxide and decanoyl peroxide. Ketoneperoxides are particularly useful and these include methyl ethyl ketoneperoxide, isobutyl methyl ketone peroxide, and 2,4-pentane dioneperoxide. Examples of peroxy ester oxidizing agents include t-butylperoctoate, t-butyl peracetate, t-butyl perbenzoate and t-amulperoctoate. Examples of alkyl peroxides include dicumyl peroxide anddi-t-butyl peroxide. Examples of hydroperoxides useful in the inventioninclude t-butyl hydroperoxide, cumene hydroperoxide, paramenthanehydroperoxide, etc. Mixtures of one or more of the above organicperoxides or hydroperoxides can be utilized with hydrogen peroxide ascuring or hardening agents or accelerators. The compositions of theinvention will contain from about 15 to about 40% or 50% by weight ofthe oxidizing agent based on the weight of said epoxy resin.

It has been found that the acid curable epoxy resins of the inventionwhich comprise a mixture of the epoxy resin and an oxidizing agent suchas a peroxide can be cured by treating said mixture with gaseous sulfurdioxide. A nearly instantaneous cure is initiated resulting in a resinhaving good strength and surface hardness which is capable as beinghandled immediately. The result is surprising, since the literature doesnot contain any description of the curing of epoxy resins in thismanner. Generally, the epoxy resin-peroxide mixture is contacted withthe sulfur dioxide gas for a period of from a fraction of a second toabout five minutes at a temperature of from ambient temperature to about150° C. In some instances, the sulfur dioxide can be suspended in astream of a carrier gas in a known manner. Examples of carrier gaseswhich are normally used for this purpose are air and nitrogen. Theamount of sulfur dioxide required to cure the epoxy resin-peroxidemixture is a catalytic amount, generally as little as about 0.5% sulfurdioxide based on the weight of the carrier gas is adequate to causepolymerization and curing. As mentioned, however, it is also feasible tocontact the epoxy-peroxide mixture directly with sulfur dioxide in theabsence of any carrier gas.

The acid curable epoxy resins of the present invention can be modifiedby the addition of various monomers and polymers which effect desirableproperties in the cured epoxy system. For example, the thermal stabilityof the epoxy system can be increased by mixing various monomers with theepoxy resin-oxidizing agent mixture. These mixtures then can be curedwith sulfur dioxide in the manner described above.

Examples of monomeric materials which can be blended with theacid-curable epoxy resins in accordance with this invention includeacrylic or vinyl monomers, furfuryl alcohol, polyfurfuryl alcohol, aformaldehyde based thermosetting resin, urethane resin, or mixturesthereof. The exact mechanism by which these specified monomers andpolymers modify the properties of the acid curable epoxy resins is notknown at this time. It has been found that up to about 50% by weight ofthe above-specified monomers and polymers can be mixed with the epoxyresin to form modified epoxy resin systems in accordance with theinvention. Acrylic compounds are particularly useful as modifiers forthe epoxy systems, and specific examples include trimethylol propanetriacrylate and furfuryl methacrylate. Examples of theformaldehyde-based thermosetting resins useful as modifiers includephenol-formaldehyde resin or urea formaldehye resin. Resorcinol also isa particularly useful modifying agent.

In one preferred embodiment of the invention, curable epoxy resincompositions are prepared comprising a mixture of

(a) a major amount of a solid particulate material, and

(b) a minor amount of (i) an acid curable epoxy resin and (ii) anoxidizing agent capable of reacting with sulfur dioxide to form acatalyst for curing said epoxy resin.

Generally, such curable epoxy resin compositions will comprise fromabout 0.2 to about 15% by weight of epoxy resin based on the weight ofthe particulate material, and the oxidizing agent will comprise fromabout 10 to about 40% by weight based on the weight of said resin. Theacid-curable epoxy resin utilized in the compositions may be modifiedepoxy resins containing up to about 50% by weight of an acrylic or vinylmonomer, furfuryl alcohol, polyfurfuryl alcohol, resorcinol, aformaldehyde based thermosetting resin, urethane resin or mixturesthereof as described above.

A variety of solid particulate materials can be utilized in the epoxyresin compositions of this embodiment. The choice of particulatematerial will depend, in part, on the intended use of the filled epoxyresin. Among the particulate materials which can be used as fillers inthe compositions of the invention include all materials containing ahigh proportion of silica such as siliceous sand, refractory materials,granular metal oxides such as zirconium oxides, and abrasive productssuch as carborundum, emery, quartz, garnet, aluminum oxide, siliconcarbide, etc.

Other materials may be included in the compositions of the invention toprovide additional desirable results. For example, coupling agents forimproving the bond between the epoxy resin and the particulate materialsand to improve the ability of the composite to return its originalproperties after prolonged aging and/or exposure to moisture. Examplesof coupling agent known in the art include the silanes and titanates.Chemically, the coupling agents are hybrid materials that possess thefunctionality of an organic reactive group at one end of the moleculeand the inorganic alkoxysilane or alkoxytitanate functionality at theother. Typical organo-functional groups found in the silanes include thevinyl, chloralkyl, epoxy, methacrylate, amine and styrylamine. Thesilane coupling agents known in the art are particularly useful in thefilled composition of the invention.

The mixtures comprising the solid particulate materials, epxoy resin,oxidizing agent and other optional additives such as silanes can beformed into various shapes utilizing molds. While the mixture is in themold, it is treated with sulfur dioxide gas to effect a nearlyinstantaneous cure as described above.

The introduction of gas into the shaped composition can be carried outby known processes in various ways depending on whether a mold or a coreis being produced. In the case of a core, for example, the compositionis shaped in its mold, which possesses orifices equipped with filters,connected to the outside, and through which the gas is introduceddirectly, under pressure, into the composition. During the production ofa mold from the composition, the reverse procedure is followed, byclamping the mixture of sand and resin on a pattern and by introducingthe gas via a plurality of channels machined in this pattern.

After manual, mechanical, hydraulic or pneumatic clamping of thecomposition consisting of granular filler, epoxy resin and oxidizingagent, the gas is injected at ambient temperature and at a pressurewhich can vary depending on the dimensions of the object to bemanufactured. The pressure must be sufficient for the gas to bedispersed uniformly throughout the entire bulk of the composition and toescape to the outside of the mold. The pressures which are usuallyemployed are between about 0.3 and 5 atmospheres. The shaped articlesprepared in this manner exhibit good strength and surface hardness andcan be handled immediately.

In this manner, foundry cores and molds can be prepared readily, and themethod offers several advantages over processes using condensation typecuring resins. One important advantage is the freedom from formaldehydein the system since most condensation resins, for example, phenolic,urea formaldehyde, furfuryl alcohol-formaldehyde, etc. liberateformaldehyde during curing. Epoxy resins do not liberate significantformaldehyde during curing. Another important advantage of thecompositions of the invention is that there is a reduced amount of waterin the system. The epoxy formulations used generally contain less thanone percent of water as compared to 2 to 8 percent in furan resins whichpreviously have been cured with sulfur dioxide. Moreover, little or nowater is liberated during the curing reaction with a ring opening andcross-linking reaction.

A further advantage of the epoxy resin compositions of the invention isthe reduction of migration of reaction by-products. In the process usingcondensation resins, there is a tendency to cure more slowly near thesurface of the mold due to absorption of the heat of reactions, andpossibly migration of reaction by-products toward the mold surfaces.When the core box temperature is below ambient temperature, this is aproblem which requires higher concentrations of peroxide to produce anarticle with sufficiently hard surface. The epoxy resin system does notappear to have the effect. Excellent core hardness is obtained even atartificially low levels of peroxide.

Further advantages are observed in the improved performance with highacid demand lake sands and improved bench life. Furan resins, forexample, perform well on low acid demand silica sands, but the basicityof high acid demand lake sands retards the cure, and higher levels ofresin and peroxide are needed. This greatly increases system costs andthe amount of organic materials in the sand. The epoxy system of thepresent invention performs much better on the sands, and in the case ofManley 1-L lake sand, a common lake sand used widely in foundryapplications, no increse in resin or peroxide is needed over thatrequired with a very low acid demand silica sand such as Wedron 5040.

The length of time the sand-resin peroxide mix can be stored, open tothe atmosphere, and still produce an acceptable article when treatedwith sulfur dioxide is termed the bench life. In the case of Manley 1-Lsand, the bench life for furan resin is 12-16 hours, depending on thesand temperature. With the epoxy system of the invention, a bench lifeof six days has been observed. Under favorable conditions, bench life ofthe furan resin is three days on a clean silica sand. With the samesand, the epoxy system of the invention has been observed to have abench life in excess of ten days.

A still further advantage of the use of the epoxy resin systems of theinvention is a substantial saving in cost, especially on high aciddemand sands where less resin is required. The average peroxide percentwith the epoxide resin is 30% whereas the furan resin requires 40 to 50%of the peroxide depending on the sand type. The epoxy process works wellwith a low cost cumene hydroperoxide catalyst. Because the epoxy systemrequires less peroxide, less sulfur dioxide is needed for catalyzation.

The following examples illustrate the compositions and processes of theinvention. Unless otherwise indicated all parts and percentages are byweight.

EXAMPLE I

A mixture of 100 parts of Epon 828 resin, a bisphenol-A type epoxyresin, and 30 parts of cumene hydroperoxide is prepared by mulling forabout five minutes. The mixture is applied as a film and heated withsulfur dioxide for about 0.5 second at ambient temperature. The initialcuring of the resin results in a slightly flexible epoxy film.

EXAMPLE II Core Binding with Epoxy Resins

In this experiment, a Wedron 5040 sand is mixed with 1.0% wt. (based onthe sand) of Epon 828 resin and mulled for three minutes. Epon 828 is abisphenol-A type epoxy resin. Cumene hydroperoxide, 30% wt. (based onthe resin weight) is added, and the mixture mulled for an additionalthree minutes. The sand-resin peroxide mix is then rammed or blown intoa mold (a standard dogbone shaped specimen mold) and treated with sulfurdioxide for about 0.5 second at room temperature, followed by a 15second air purge. Gassing times of about 0.3 seconds to about 5 minutesand temperatures from room temperature to about 150° C. can be used.

The initial cure of the epoxy system is characterized by a tough,slightly flexible cure. The flexiblity is an advantage in manyapplications, resulting in reduced core breakage upon removal of thearticle from the mold. In some cases, however, a rigid initial cure ispreferred to prevent deformation of thin, intricate designs. It has beenfound that modification of the epoxy resin with 5-15%phenol-formaldehyde resin results in a more rigid initial cure andhigher initial tensile strength.

The product obtained after 20 seconds, as described above, is capable ofbeing handled immediately. This product has equal or better hardness andtensile strength than a like product made using condensation typeresins.

This procedure also may be repeated using bisphenol-F type epoxy resinsand epoxy novolac resins.

EXAMPLE III Core Binding with Modified Epoxy Resin

In another experiment, a Wedron 5040 sand is mixed with 1.0% wt. (basedon the sand) of Epon 828 resin modified with 15% furfuryl alcohol (orfurfuryl alcohol-formaldehyde polymer) and mulled for three minutes.Cumene hydroperoxide, 30% wt. (based on the resin weight) is added andthe mixture mulled for an additional three minutes. Thesand-resin-peroxide mix is then rammed or blown into a mold (a standarddogbone shaped specimen mold) and gassed with sulfur dioxide for about0.5 second at room temperature, followed by a 15 second air purge.Gassing times of about 0.3 seconds to about 5 minutes and temperaturesfrom room temperature to about 150° C. can be used.

The product obtained after 20 seconds, as described above, is capable ofbeing handled immediately. This product has equal or better hardness andtensile strength than a like product made using condensation typeresins.

This procedure may be repeated using bisphenol-F type epoxy resins andepoxy novolac resins.

EXAMPLE IV Baking of Epoxy Bonded Cores

The specimens produced in Examples II and III are baked in a mufflefurnace at 990° C. After two minutes the biscuits are removed and tappedwith a small hammer to determine ease of breakage. The furfuryl alcohol(or furfuryl alcohol-formaldehyde) composition is noticeably harder.These experiments indicate that an increase in thermal stability resultsfrom modification of the epoxy with furfuryl alcohol or furfurylalcohol-formaldehyde resin.

EXAMPLE V Core Binding with Furfuryl Alcohol Modified Epoxy

A Wedron 5040 sand is mixed with 1.0% wt. (based on the sand) of Epon828 resin modified with 15% furfuryl alcohol and mulled for threeminutes. Cumene hydroperoxide 30% wt. (based on the resin weight) isadded, and the mixture mulled for an additional three minutes. Thesand-resin-peroxide mix is then rammed or blown into a mold (a standarddogbone shaped specimen mold) and gassed with sulfur dioxide for about0.5 second at room temperature, followed by a 15 second air purge.Gassing times of about 0.3 seconds to about 5 minutes and temperaturesfrom room temperature to about 150° C. can be used. The specimen orbiscuit is then heated for a further period of five minutes at 110° C.

After cooling to room temperature, the biscuit has a tensile strength of575 psi as compared to 290 psi without baking.

This procedure may be repeated using bisphenol-F type epoxy resins andepoxy novolac resins.

EXAMPLE VI Core Binding with Modified Epoxy Resin

A Wedron 5040 sand is mixed with 1.0% wt. (based on the sand) ofmodified Epon 828 resin and mulled for three minutes. The compositionused is: 80% Epon 828, 10% Phenolic resin, 0.2 A-187 Silane, 10%methanol to which there is added 20% trimethylolpropane triacylate. Thephenolic resin used in this and the following examples is a resole witha 1.5:1 formaldehyde to phenol ratio reacted under basic conditions.Cumene hydroperoxide 30% wt. (based on the resin weight) is added andthe mixture mulled for an additional three minutes. Thesand-resin-peroxide mix is then rammed or blown into a mold (a standarddogbone shaped specimen mold) and gassed with sulfur dioxide for about0.5 second at room temperature, followed by a 20 second air purge.Gassing times of about 0.3 seconds to about 5 minutes and temperaturesfrom room temperature to about 150° C. can be used.

The product obtained after 20 seconds, as described above, is capable ofbeing handled immediately. The product has an immediate tensile strength(after 20 seconds) of 156 psi as compared to 130 psi for the unmodifiedproduct. This product has equal or better hardness and tensile strengththan a like product made using condensation type resins.

The procedure may be repeated using bisphenol-F type epoxy resins andepoxy novolac resins.

EXAMPLE VII Core Binding with Modified Epoxy Resin

A Wedron 5040 sand is mixed with 1.0% wt. (based on the sand) ofmodified Epon 828 resin and mulled for three minutes. The compositionused is: 80% Epon 828, 10% phenolic resin, 0.2 A-187 Silane, 10%methanol to which there was added 20% furfuryl methacrylate. Cumenehydroperoxide, 30% wt. (based on the resin weight) is added and themixture mulled for an additional three minutes. The sand-resin-peroxidemix is then rammed or blown into a mold (a standard dogbone shapedspecimen mold) and gassed with sulfur dioxide for about 0.5 second atroom temperature, followed by a 20 second air purge. Gassing times ofabout 0.3 seconds to about 5 minutes and temperatures from roomtemperature to about 150° C. can be used.

The product obtained after 20 seconds, as described above, is capable ofbeing handled immediately. The product has an immediate tensile strengthsubstantially greater than the unmodified product. This product hasequal or better hardness and tensile strength than a like product madeusing condensation type resins.

The procedure may be repeated using bisphenol-F type epoxy resins andepoxy novolak resins.

EXAMPLE VIII Core Binding with Modified Epoxy Resin

A Wedron 5040 sand is mixed with 1.0% wt. (based on the sand) ofmodified Epon 828 resin and mulled for three minutes. The compositionused is: 80% Epon 828, 10% phenolic resin, 0.2 A-187 Silane, 10%methanol to which there was added 20% furfuryl glycidyl ether. Thefurfuryl glycidyl ether is prepared by reacting epichlorohydrin withfurfuryl alcohol using a base such as sodium hydroxide as catalyst andfor dehydrohalogenation. Cumene hydroperoxide, 30% wt. (based on theresin weight) is added, and the mixture mulled for an additional threeminutes. The sand-resin-peroxide mix is then rammed or blown into a mold(a standard dogbone shaped specimen mold) and gassed with sulfur dioxidefor about 0.5 second at room temperature, followed by a 20 second airpurge. Gassing times of about 0.3 seconds to about 5 minutes andtemperatures from room temperature to about 150° C. can be used.

The product obtained after 20 seconds, as described above, is capable ofbeing handled immediately. The product has an immediate tensile strengthsubstantially greater than the unmodified product. This product hasequal or better hardness and tensile strength than a like product madeusing condensation type resins. Sand/resin compositions of this typealso have improvied thermal stability.

The procedure may be repeated using bisphenol-F type epoxy resins andepoxy novolac resins.

EXAMPLE IX

In a series of experiments, a Manley 1-L sand is mixed with 1.0% wt.(based on the sand) of modified Epon 828 resin and mulled for threeminutes. The composition used is 82% Epon 828, 5% resorcinol resin, 3%triphenyl phosphite, 0.2 A-187 Silane, 10% methanol. Cumenehydroperoxide 30% wt. (based on the resin weight) is added and themixture mulled for an additional three minutes. The sand-resin-peroxidemix is held for periods of 5 minutes, 65 hours, and 6 days,respectively, rammed or blown into a mold (a standard dogbone shapedspecimen mold) and gassed with sulfur dioxide for about 0.5 second atroom temperature, followed by a 15 second air purge. Gassing times ofabout 0.3 seconds to about 5 minutes and temperatures from roomtemperature to about 150° C. can be used.

The tensile and hardness data for these products are taken after thefollowing periods of time:

    ______________________________________                                        Age of Mix  5 mins.      65 hrs. 6 days                                       ______________________________________                                        20 sec.                                                                       Tensile psi 108          80      80                                           Core hardness                                                                              88          79      77                                           30 min.                                                                       Tensile psi 279          200     190                                          Core hardness                                                                              91          88      85                                           24 hrs.                                                                       Tensile psi 280          260     240                                          Core hardness                                                                              92          90      86                                           ______________________________________                                    

The procedure may be repeated using bisphenol-F type epoxy resins andepoxy novolac resins.

EXAMPLE X

In another series of experiments, a 504 Wedron sand is mixed with 1.0%wt. (based on the sand) of modified Epon 828 resin and mulled for threeminutes. The composition used is: 82% Epon 828, 5% resorcinol resin, 3%triphenyl phosphite, 0.2 A-187 Silane, 10% methanol. Cumemehydroperoxide 30% wt. (based on the resin weight) is added and themixture mulled for an additional three minutes. The sand-resin-peroxidemix is held for periods of 5 minutes, 65 hours, and 6 days, respectivelyand then rammed or blown into a mold (a standard dogbone shaped specimenmold) and gassed with sulfur dioxide for about 0.5 second at roomtemperature, followed by a 15 second air purge. Gassing times of about0.3 seconds to about 5 minutes and temperatures from room temperature toabout 150° C. can be used.

The tensile and hardness data for these products are as follows:

    ______________________________________                                        Age of Mix  5 mins.      65 hrs. 6 days                                       ______________________________________                                        20 sec.                                                                       Tensile psi 110          108     109                                          Core hardness                                                                              93           90      84                                          30 min.                                                                       Tensile psi 280          240     255                                          Core hardness                                                                              99           97      88                                          24 hrs.                                                                       Tensile psi 278          276     280                                          Core hardness                                                                              98           96      88                                          ______________________________________                                    

The procedures may be repeated using Bisphenol-F type epoxy resins andepoxy novolac resins.

EPOXY RESINS VS. FURAN RESINS OF LAKE SAND

A series of experiments is carried out evaluating the products obtainedby the binding of lake sand with epoxy resin and with furan resin atvarious levels.

EXAMPLE XI

In this series of experiments, a Manley 1-L lake sand is mixed withresin and mulled for three minutes. Then, the peroxide is added and themixture mulled for an additional three minutes. This procedure isrepeated for an epoxy resin and for a furan resin at three differentlevels and for two different peroxides. The sand-resin-peroxide mix isthen rammed or blown into a mold (a standard dogbone shaped specimenmold) and gassed with sulfur dioxide for about 0.5 second at roomtemperature, followed by a 15 second air purge. Gassing times of about0.3 seconds to about 5 minutes and temperatures from room temperature toabout 150° C. can be used.

The epoxy resin used in Epon 828 in admixture with other materials. Thecomposition used is: 82% Epon 828, 5% resorcinol resin, 3% triphenylphosphite, 0.2 A-187 Silane, 10% methanol. The peroxide, 30% wt. (basedon the resin weight) is added and the mixture mulled for an additionalthree minutes before molding. The furan resin is a furfurylalcohol-formaldehyde copolymer reacted under acidic conditions. Theformaldehyde to furfuryl alcohol ratio is 1.

The tensile and hardness data for the products using the differentresins and the different peroxides are as follows:

    ______________________________________                                        Resin     Epoxy     Furan    Furan    Furan                                   ______________________________________                                        % (BOS)   1.0       1.0      1.25     1.5                                     Peroxide  Cumene         Methylethyl ketone                                             Hydroperoxide  peroxide                                             % (BOR)   30        30       45       45                                      Sand       Manley 1-L                                                         Temp. °F.                                                                        77        77       76       76                                      20 sec.                                                                       Tensile psi                                                                             108       74       88       120                                     Core hardness                                                                           88        45       69       82                                      30 min.                                                                       Tensile psi                                                                             279       88       123      196                                     Core hardness                                                                           91        46       74       83                                      24 hrs.                                                                       Tensile psi                                                                             274       92       135      171                                     Core hardness                                                                           91        35       81       86                                      ______________________________________                                         BOS = based on sand                                                           BOR = based on resin                                                     

The procedure may be repeated using Bisphenol-F type epoxy resins andepoxy novolac resins.

Evaluation of Different Epoxy Resin-Sand-Peroxide Mixes EXAMPLE XII

In this series of experiments, a 5040 Wedron silica sand is mixed withresin and mulled for three minutes. The peroxide is added and themixture mulled for an additional three minutes. This procedure isrepeated for two epoxy resin compositions and at two different levelsand for two different peroxides. The sand-resin-peroxide mix is thenrammed or blown into a mold (a standard dogbone shaped specimen mold)and gassed with sulfur dioxide for about 0.5 second at room temperature,followed by a 15 second air purge. Gassing times of about 0.3 seconds toabout 5 minutes and temperatures from room temperature to about 150° C.can be used.

The epoxy resin used is Epon 828 in admixture with other materials.Composition A is: 80% Epon 828, 15% furfuryl alcohol, 5% resorcinolresin, 0.2 A-187 Silane. Composition B is: 82% Epon 828, 5% resorcinolresin, 3% triphenyl phosphite, 0.2 A-187 Silane, 10% methanol. Cumenehydroperoxide, 30% wt. (based on the resin weight) is added, and themixture mulled for an additional three minutes before molding.

The tensile and hardness data for the products using the differentresins and the different peroxides are as follows:

    ______________________________________                                        RESIN       A            B       B                                            ______________________________________                                        % (BOS)      1.0          1.0     0.7                                         Peroxide     Cumene Hydroperoxide                                             % (BOR)     30           30      30                                           Sand         5040 Wedron                                                      Temp. °F.                                                                          76           76      77                                           20 sec.                                                                       Tensile psi 70           110     90                                           Core hardness                                                                             89           93      78                                           30 min.                                                                       Tensile psi 186          280     180                                          Core hardness                                                                             92           99      85                                           24 hrs.                                                                       Tensile psi 268          279     220                                          Core hardness                                                                             96           99      96                                           ______________________________________                                         BOS = based on sand                                                           BOR = based on resin                                                     

The procedure may be repeated using Bisphenol-F type epoxy resins andepoxy novolac resins.

EXAMPLE XIII

In this series of experiments, a Manley 1-L lake sand is mixed withresin and mulled for three minutes. The peroxide is added, and themixture mulled for an additional three minutes. This procedure isrepeated for different epoxy resin compositions at the same level andfor two different peroxides. The sand-resin-peroxide mix is then rammedor blown into a mold (a standard dogbone shaped specimen mold) andgassed with sulfur dioxide for about 0.5 second at room temperature,followed by a 15 second air purge. Gassing times of about 0.3 seconds toabout 5 minutes and temperatures from room temperature to about 150° C.can be used.

The epoxy resin used is Epon 828 in admixture with other materials.Composition B is: 82% Epon 828, 5% resorcinol resin, 3% triphenylphosphite, 0.2 A-187 Silane, 10% methanol. Composition C is 80% Epon828, 15% methanol, 5% resorcinol and 0.2% A-187 Silane. The peroxide,30% wt. (based on the resin weight) is added and the mixture mulled foran additional three minutes before molding.

The tensile and hardness data for the products using the differentresins and the different peroxides are as follows:

    ______________________________________                                        RESIN       B             C      B                                            ______________________________________                                        % (BOS)      1.0           1.0     1.0                                        Peroxide    60% H.sub.2 O.sub.2                                                                         CH     MEKP                                         % (BOR)     15            30     30                                           Temp. °F.                                                                          76            77     75                                           20 sec.                                                                       Tensile psi.                                                                              50            116    70                                           Core hardness                                                                             10            81     65                                           30 min.                                                                       Tensile psi 50            200    86                                           Core hardness                                                                             12            82     78                                           24 hrs.                                                                       Tensile psi 40            270    148                                          Core hardness                                                                             10            86     95                                           ______________________________________                                         BOS = based on sand                                                           BOR = based on resin                                                          CH = cumene hydroperoxide                                                     MEKP = methylethyl ketone peroxide                                       

The procedure may be repeated using Bisphenol-F type epoxy resins andepoxy novolac resins.

EXAMPLE XIV

In this series of experiments, the sand is mixed with resin and mulledfor three minutes. The peroxide is added, and the mixture mulled for anadditional three minutes. This procedure is repeated for three differentsands, three different epoxy resin compositions and at two differentlevels. Cumene hydroperoxide is used. The sand-resin-peroxide mix isthen rammed or blown into a mold (a standard dogbone shaped specimenmold) and gassed with sulfur dioxide for about 0.5 second at roomtemperature, followed by a 15 second air purge. Gassing times of about0.3 seconds to about 5 minutes and temperatures from room temperature toabout 150° C. can be used.

The epoxy resin used is Epon 828 in admixture with other materials.Composition D is: 75% Epon 828, 15% furfuryl alcohol polymer 0.2% A-187Silane, 10% methanol. Composition B is: 82% Epon 828, 5% resorcinolresin, 3% triphenyl phosphite, 0.2% A-187 Silane, 10% methanol.Composition E is 80% Epon 828, 10% phenolic resin, 0.2 A-187 Silane, 10%methanol. Cumene hydroperoxide, 30% wt. (based on the resin weight) isadded, and the mixture mulled for an additional three minutes beforemolding.

The tensile and hardness data for the products using the different resincompositions and the different sands are as follows:

    ______________________________________                                        RESIN     B           D          E                                            ______________________________________                                        % (BOS)    0.8         1.0        1.0                                         Peroxide   Cumene Hydroperoxide                                               % (BOR)   30          30         30                                           Sand      Florida Zircon                                                                            Manley 1-L 5040 Wedron                                  Temp. °F.                                                                        75          77         78                                           20 sec.                                                                       Tensile psi                                                                             112         98         136                                          Core hardness                                                                           99          86         88                                           30 min.                                                                       Tensile psi                                                                             260         140        278                                          Core hardness                                                                           98          85         91                                           24 hrs.                                                                       Tensile psi                                                                             390         230        296                                          Core hardness                                                                           100         86         89                                           ______________________________________                                         BOS = based on sand                                                           BOR = based on resin                                                     

The procedure may be repeated using Bisphenol-F type epoxy resins, epoxynovolac resins, furfuryl glycidyl ether, etc.

EXAMPLE IV

A Wedron 5040 sand is mixed with 1.0% by weight (based on the weight ofthe sand) of Epon 828 resin modified with 20% of trimethylolpropanetriacrylate (TMPTA) blended with 10% of methanol and 0.2% A-187 Silaneand mulled for about three minutes. Cumene hydroperoxide, 30% wt. (basedon the resin weight) is added and the mixture mulled an additional threeminutes. The mixture is rammed or blown into a standard dogbone shapedspecimen mold and gassed with sulfur dioxide for about 0.5 second atambient temperature followed by a 15 second air purge. The tensile andhardness data for the specimens are taken after the following periods oftime. For comparison, the above procedure is repeated using Epon 828without the triacylate but with 30% of the peroxide.

    ______________________________________                                                           TMPTA                                                                  Epon 828                                                                             modified Epon 828                                          ______________________________________                                        20 sec.                                                                       Tensile psi   136      233                                                    Core hardness  88      91                                                     30 min.                                                                       Tensile psi   270      320,384                                                Core hardness  90      90                                                     24 hour                                                                       Tensile psi   269      334,380                                                Core hardness  89      88                                                     ______________________________________                                    

As can be seen above, the modification of the bisphenol-A epoxy resinformulation with 20% of the triacrylate increases the tensile strengthby 75% in the first 20 seconds after gassing. In addition the rigidityof the article is greatly increased thereby permitting fabrication ofthin sectioned complex cores such as water jacket and cylinder headcores. Another advantage is that the peroxide concentration needed forcuring is reduced.

EXAMPLE XVI

A Wedron sand is mixed with 1.0% by weight (based on weight of the sand)of a mixture comprising 75 parts of an epoxy-novolac resin (EPN-1139from Ciba Geigy) and 25 parts of Epon 828 blended with 10 methanol at0.2% A-187 Silane. Specimens are prepared as described in Example XVusing this formulation and similar formulation except that the peroxideis reduced to 20% and 7% of trimethylolpropane triacylate (TMPTA) isadded to the formuation. For comparison specimens of unmodified Epon 828also are prepared. The tensile and hardness data for specimens preparedin this example are as follows:

    ______________________________________                                                                     Epon 828:                                                           Epon 828  EPN 1139:                                                  Epon 828 EPN 1139  TMPTA                                            ______________________________________                                        20 sec.                                                                       Tensile psi 136        224       214                                          Core hardness                                                                             88         82        92                                           5 min.                                                                        Tensile psi --         294       380                                          Core hardness                                                                             --         82        96                                           30 min.                                                                       Tensile psi 270        350       428                                          Core hardness                                                                             90         82        96                                           24 hour                                                                       Tensile psi 269        338       495                                          Core hardness                                                                             89         85        92                                           ______________________________________                                    

The above results demonstrate that the blend of epoxy and epxoy novolacproduces stronger cores than the epoxy alone. It also has been foundthat the blend produces stronger cores than the epoxy novolac alone. Thedata also shows the improved results when the epoxy resin blend ismodified with the TMPTA even when the amount of peroxide is reduced.

EXAMPLE XVII

A Wedron sand is mixed with 1.0% by weight (based on weight of the sand)of either an epoxy novolac resin (EPN-1139) containing only 10% methanoland 0.2% of A-187 Silane or a blend of 45% epoxy novolac resin EPN-1139with 45% Epon 828 and 0.2% A-187 Silane and 10% methanol. Cumenehydroperoxide (30% wt.) is mulled into the resin formulations andspecimen shapes are prepared as in Example XV. The tensile and corehardness data are as follows:

    ______________________________________                                                             EPN-1139:                                                           EPN-1139  Epon 828                                                 ______________________________________                                        20 sec.                                                                       Tensile psi  160,182     162,168                                              Core hardness                                                                              85,89       88,86                                                30 min.                                                                       Tensile psi  182         334                                                  Core hardness                                                                               84          92                                                  48 hour                                                                       Tensile psi  210         372                                                  Core hardness                                                                               80          93                                                  ______________________________________                                    

The above data shows the superior strengths obtained when thecombination of resins is used in the compositions of this invention.

It also has been found that various other binder resins normally used inthe preparation of foundry molds and cores utilizing the combination ofan oxidizing agent and sulfur dioxide as the curing agent can beimproved by initially blending said resins with minor amounts of acidcurable epoxy resins of the type described above. More specifically, ithas been discovered that the strength of molds and cores preparedutilizing, for example, ethylenically unsaturated monomer bindermaterials such as described in British Pat. No. 2,066,714 which aregenerally monofunctional, difunctional, trifunctional andtetrafunctional acrylates; and acid-curing condensation type resinscomprising a polyfurfuryl alcohol such as described in U.S. Pat. No.4,176,114 can be increased by the incorporation of minor amounts, thatis, up to about ;b 50% by weight, of acid curing epoxy resins. Thefollowing example illustrates this embodiment.

EXAMPLE XVIII

An acrylic resin is prepared by combining 2.5 moles of acrylic acid, 1mole of diethylene glycol, 3 grams of concentrated sulfuric acid and 0.3gram of hydroquinone. The mixture is reacted at about 95° C. in thepresence of air for 3 hours. The mixture then is washed with distilledwater, and the excess water is removed by vacuum distillation.

A portion of this acrylate product is modified with 30% by weight ofEpon 828 resin and 0.2% of Z-6075 Silane. Another portion is modifiedonly with 0.2% of Z-6075. Z-6075 is vinyl triacetoxysilane manufacturedby Dow Corning.

Twenty grams of the Epon 828 modified acrylic is mixed with 2,000 gramsof Wedron 5040 silica for two minutes in a Hobart mixer at low speed.Cumene hydroperoxide (1.6 grams) then is added and similarly mixed.Standard dogbone tensile specimens are prepared and gassed with 100%sulfur dioxide for 0.5 second. The 20 second tensile strength of thespecimen is 120 psi with a core hardness of 85, and the 5 minute tensilestrength if 150 psi with 85 core hardness.

A similar test on specimens prepared from the acrylate modified with thesilane (no Epon 828) exhibits a 20 second tensile strength of 80 psiwith a core hardness of 65, and a 5 minute tensile strength of 90 psiwith a 65 core hardness. The above results demonstrate that the tensilestrength of acrylic resins used in the sulfur dioxide process can beincreased by modifying the acrylic resin with an acid curable epoxyresin. Similar results are obtained when furan resins are modified withminor amounts of acid curable epoxy resin.

I claim:
 1. A curable binder composition comprising a mixture of(a) amajor amount of a free radical curable ethylenically unsaturated bindermaterial, (b) from 30 percent to 50 percent by weight of an epoxy resin,and (c) an oxidizing agent capable of reacting with sulfur dioxide toform a catalyst for curing said resin mixture, said percent by weight of(b) being based upon the total weight of (a) and (b).
 2. The compositionof claim 1 wherein the oxidizing agent is a peroxide.
 3. The compositionof claim 1 wherein the epoxy resin is selected from the group consistingof (1) mixed aliphatic-aromatic epoxy resins derived from abis(hydroxy-aromatic) alkane or a tetrakis(hydroxy-aromatic) akane witha halogen-substituted aliphatic epoxide, (2) novolac resins, and (3)aliphatic epoxy resins.
 4. The composition of claim 3 wherein theethylenically unsaturated binder material is a monomer.
 5. Thecomposition of claim 4 wherein the ethylenically unsaturated monomer isa monofunctional, diffunctional, trifunctional or tetrafunctionalacrylate.
 6. The compositions of claim 5 wherein the epoxy resin is aglycidyl ether of bisphenol A, B, F, G, or H.
 7. The composition ofclaim 6 wherein the peroxide is methyl ethyl ketone peroxide, cumenehydroperoxide, paramenthane hydroperoxide, t-butyl hydroperoxide,diisopropyl benzene hydroperoxide, admixtures thereof or admixturesthereof with hydrogen peroxide.
 8. A curable molding compositioncomprising a mixture of a major amount of a solid particulate material,and a minor amount of a binder composition comprising a mixture of(a) amajor amount of a free radical curable ethylenically unsaturated bindermaterial, (b) from 30 percent to 50 percent by weight of an epoxy resin,and (c) an oxidizing agent capable of reacting with sulfur dioxide toform a catalyst for curing said resin mixture, said percent by weight of(b) being based upon the total weight of (a) and (b).
 9. The compositionof claim 8 wherein the oxidizing agent is a peroxide.
 10. The moldingcomposition of claim 9 wherein the epoxy resin is selected from thegroup consisting of (1) mixed aliphatic-aromatic epoxy resins derivedfrom a bis(hydroxy-aromatic) alkane or a tetrakis(hydroxy-aromatic)alkane with a halogen-substituted aliphatic epoxide, (2) novolac resins,and (3) aliphatic epoxy resins.
 11. The composition of claim 10 whereinthe ethylenically unsaturated binder material is a monomer.
 12. Thecomposition of claim 11 wherein the ethylenically unsaturated monomer isa monofunctional, difunctional, trifunctional or tetrafunctionalacrylate.
 13. The composition of claim 12 wherein the epoxy resin is aglycidyl ether of bisphenol A, B, F, G, or H.
 14. The composition ofclaim 13 wherein the peroxide is methyl ethyl ketone peroxide, cumenehydroperoxide, paramenthane hydroperoxide, t-butyl hydroperoxide,diisopropyl benzene hydroperoxide, admixtures thereof or admixturesthereof with hydrogen peroxide.
 15. The composition of claim 14 whereinthe solid particulate filler comprises inorganic abrasive particles. 16.The composition of claim 15 wherein the solid particulate fillercomprises sand.
 17. A method of curing binder compositions containing atleast one epoxy resin which comprises the steps of(a) preparing amixture curable with gaseous sulfur dioxide comprising(i) a major amountof a free radical curable ethylencially unsaturated binder material,(ii) from 30 percent to 50 percent by weight an epoxy resin, and (iii)an oxidizing agent capable of reacting with sulfur dioxide to form acatalyst for curing said resin mixture, said percent by weight of (a)(ii) being based upon the total weight of (a) (i) and (a) (ii), and (b)contacting said mixture with gaseous sulfur dioxide.
 18. The method ofclaim 17 wherein the oxidizing agent is a peroxide.
 19. The method ofclaim 18 wherein the epoxy resin is selected from the group consistingof (1) mixed aliphatic-aromatic epoxy resins derived from abis(hydroxy-aromatic) alkane or a tetrakis(hydroxy-aromatic) alkane witha halogen-substituted aliphatic epoxide, (2) novolac resins, and (3)aliphatic epoxy resins.
 20. The method of claim 19 wherein theethylenically unsaturated binder material is a monomer.
 21. Thecomposition of claim 20 wherein the ethylenically unsaturated monomer isa monofunctional, difunctional, trifunctional or tetrafunctionalacrylate.
 22. The method of claim 21 wherein the epoxy resin is aglycidyl ether of bisphenol A, B, F, G, or H.
 23. The method of claim 22wherein said peroxide is methyl ethyl ketone peroxide, cumenehydroperoxide, paramenthane hydroperoxide, t-butyl hydroperoxide,diisopropyl benzene hydroperoxide, admixtures thereof or admixturesthereof with hydrogen peroxide.
 24. The method of claim 20 wherein themixture is contacted with sulfur dioxide for a period of from a fractionof a second to about five minutes at a temperature of from ambienttemperature to about 150° C.
 25. A method of forming foundry's shapeswhich comprises the steps of(a) mixing a major amount of solidparticulate material with a minor amount of a binder compositioncomprising a mixture of(i) a major amount of a free radical curableethylenically unsaturated binder material, (ii) from 30 percent to 50percent by weight of an epoxy resin, said percent by weight of (a) (ii)being based upon the total weight of (a) (i) and (a) (ii), and(iii) anoxidizing agent capable of reacting with sulfur dioxide to form acatalyst for curing said mixture, (b) forming said mixture into thedesired shape, and (c) contacting said formed mixture with sulfurdioxide for a period of from a fraction of a second to about fiveminutes at a temperature of from room temperature to about 150 degreesC. to effect resin cure.
 26. The method of claim 25 wherein theoxidizing agent is a peroxide.
 27. The method of claim 26 wherein theepoxy resin is selected from the group consisting of (1) mixedaliphatic-aromatic epoxy resins derived fromm a bis(hydroxy-aromatic)alkane or a tetrakis(hydroxy-aromatic) alkane with a halogen-substitutedaliphatic epoxide, (2) novolac resins, and (3) aliphatic epoxy resins.28. The method of claim 27 wherein the ethylenically unsaturated bindermaterial is a monomer.
 29. The method of claim 28 wherein theethylenically unsaturated monomer is a monofunctional, difunctional,triflunctional or tetrafunctional acrylate.
 30. The method of claim 29wherein the epoxy resin is a glycidyl ether of bisphenol A, B, F, G, orH.
 31. The method of claim 30 wherein the peroxide is methyl ethylketone peroxide, cumene hydroperoxide, paramenthane hydroperoxide,t-butyl hydroperoxide, diisopropyl benzene hydroperoxide, admixturesthereof or admixtures thereof with hydrogen peroxide.
 32. The method ofclaim 31 wherein the solid particulate material is sand.
 33. The methodof claim 32 wherein the formed shape, after contact with sulfur dioxide,is purged with air or inert gas and baked at an elevated temperature.